Earthmoving equipment is used to perform a variety of operations, including loading, or capturing, material, such as soil, at one location and dumping, or depositing, the material at another location. For example, such material movement may be employed to adjust elevations at a project site. Scrapers, which typically provide quick load, dump, and maneuver time, may be used to perform such operations, and generally include a machine having a bowl within which material may be captured, and a cutting edge located adjacent a cut opening of the bowl. Although various scraper configurations are available, scrapers are often pulled by a tractor, such as a wheeled or track type tractor. In addition, scrapers may provide their own fraction via a separate engine that applies rim pull, or power, to the wheels of the scraper. Such machines, including both tractor and scraper powertrains, may be referred to as dual powertrain machines.
Conventional methods for limiting the speed of a dual powertrain machine include limiting the top gear in which the tractor powertrain, or primary powertrain, may operate. For example, a gear that may produce a maximum machine speed at or below a machine speed limit may be selected as the top operating gear for the primary powertrain. For powertrains having multiple forward gears, this speed limiting method limits the selection of machine speed limits to a discrete number of maximum speed limits corresponding to the number of gears. Thus, while potentially effective, this method does not allow a wide selection of maximum machine speeds and, further, may be inefficient, particularly when the transmission could operate at a lower engine speed in a higher gear while still maintaining a machine speed below the machine speed limit.
U.S. Pat. No. 6,030,315 to Bellinger discusses a “hold mode” transmission operating condition for a single powertrain machine in which the currently engaged gear is maintained and, further, teaches a system for overriding the hold mode operating condition if such operation is determined to be inappropriate based on a vehicle operating parameter. Although the Bellinger reference teaches other useful applications of the hold mode condition, in addition to machine speed limiting, it recognizes the potential inefficiencies of such a condition and seeks to override the hold mode condition in certain scenarios. Thus, in addition to the inefficiencies cited by Bellinger, a gear hold feature, particularly when used for machine speed limiting, may reduce efficiency, increase fuel consumption, and potentially increase engine wear.
The present disclosure is directed to one or more of the problems set forth above.